1. Field of the Invention
The invention relates to a method and a correspondingly configured communications unit, in particular of a motor vehicle, for detecting communications problems in vehicle-to-environment communication in an ISM radio band.
2. Prior Art
The ISM radio band is a radio band that can be used without a license by devices in the industrial, scientific and medical sector provided that the specifications, in particular with respect to the duty cycle, are complied with. In this case, the abbreviation ISM stands for “Industrial, Scientific and Medical”. The license-free ISM radio band is also used, in particular, by wireless access and driving authorization communication in motor vehicles, which is also called “RKE (Remote Keyless Entry)”. Frequency bands at 434 MHz and 868 MHz with transmission powers of 10 dBm and 14 dBm, respectively, are available in the European Union as the RKE communications band. Further typical communications bands are the band around 2.4 GHz and the band at 5 GHz, which are primarily used for WLAN, Bluetooth, etc.
The present invention can generally be used in radio bands that are not provided with overload monitoring with congestion control. This also applies, in particular, to the communications protocols of the license-free ISM radio bands.
WO 2009/074655 A1 discloses a method for transmitting vehicle-relevant data relating to a vehicle via mobile communications devices, in which two different communications paths are used. A first communications path is WLAN-based communication. The second communications path is formed by “ignition key” communication, which takes place in a license-free ISM band.
However, there is the problem that the frequency bands of license-free ISM communication are also used by a large number of other communications devices. In motor vehicles, these include, for example, a tire pressure monitoring system (TPMS), baby monitors, radio headphones, consumption recording systems and the like. In urban environments in particular, the radio channel may therefore be so highly utilized that proper communication is no longer possible.